Rhythm discrimination enhancement - av drive

ABSTRACT

An apparatus comprises an implantable cardiac signal sensing circuit and a controller circuit. The implantable cardiac signal sensing circuit provides a sensed depolarization signal from a ventricle and a sensed depolarization signal from an atrium. The controller circuit includes a one-to-one detector circuit and a tachyarrhythmia discrimination circuit. The one-to-one detector circuit measures cardiac depolarization intervals of the atrium and the ventricle and determines whether a relationship of atrial depolarizations to ventricular depolarizations is substantially one-to-one. The tachyarrhythmia discrimination circuit increments a counter when detecting a shortening or prolonging of a V-V interval that immediately precedes the same shortening or prolonging of an A-A interval, classifies the episode as VT according to the counter, and provides the classification of the tachyarrhythmia episode to a user or process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/371,398, filed on Aug. 6, 2010, under 35 U.S.C. §119(e), which isincorporated herein by reference in its entirety.

BACKGROUND

Implantable medical devices (IMDs) include devices designed to beimplanted into a patient. Some examples of these devices include cardiacfunction management (CFM) devices such as implantable pacemakers,implantable cardioverter defibrillators (ICDs), cardiacresynchronization therapy devices (CRTs), and devices that include acombination of such capabilities. The devices can be used to treatpatients using electrical or other therapy or to aid a physician orcaregiver in patient diagnosis through internal monitoring of apatient's condition. The devices may include one or more electrodes incommunication with one or more sense amplifiers to monitor electricalheart activity within a patient, and often include one or more sensorsto monitor one or more other internal patient parameters. Other examplesof implantable medical devices include implantable diagnostic devices,implantable drug delivery systems, or implantable devices with neuralstimulation capability.

Additionally, some IMDs detect events by monitoring electrical heartactivity signals. In CFM devices, these events can include heart chamberexpansions or contractions. By monitoring cardiac signals indicative ofexpansions or contractions, IMDs can detect abnormally slow heart rate,or bradycardia. Some IMDs detect abnormally rapid heart rate, ortachyarrhythmia. Tachyarrhythmia includes ventricular tachycardia (VT)and supraventricular tachycardia (S VT). Tachyarrhythmia also includesrapid and irregular heart rate, or fibrillation, including ventricularfibrillation (VF).

When detected, ventricular tachyarrhythmia can be terminated withhigh-energy shock therapy delivered with an ICD.Cardioversion/defibrillation therapy can cause patient discomfort andconsumes a relatively large amount of battery power which may lead to ashortened useful device lifetime.

Overview

This document relates generally to systems, devices, and methods formonitoring cardiac electrophysiological parameters of a patient orsubject. Episodes of atrial and ventricular tachyarrhythmia are alsomonitored.

An apparatus example includes an implantable cardiac signal sensingcircuit, configured to provide a sensed depolarization signal from aventricle and a sensed depolarization signal from an atrium; and acontroller circuit communicatively coupled to the implantable cardiacsignal sensing circuit. The controller circuit includes a one-to-onedetector circuit and a tachyarrhythmia discrimination circuit. Theone-to-one detector circuit is configured to measure cardiacdepolarization intervals of the atrium and the ventricle and determinewhether a relationship of atrial (A-A) depolarizations to ventricular(V-V) depolarizations is substantially one-to-one. The tachyarrhythmiadiscrimination circuit is configured to detect an episode oftachyarrhythmia while the relationship atrial depolarizations toventricular depolarizations is substantially one-to-one, increment afirst counter when detecting one of a shortening or prolonging of a V-Vinterval that is immediately preceded by the same one of a detectedshortening or prolonging of an A-A interval during the episode,increment a second counter when detecting one of a shortening orprolonging of an A-A interval during the episode that is immediatelypreceded by the same one of a shortening or prolonging of a V-V intervaland an interval from a ventricular depolarization to an atrialdepolarization (V-A) is greater than a specified threshold V-A intervalvalue, classify the episode as VT when the count of the second counterexceeds the count of the first counter by a specified threshold count,and provide the classification of the tachyarrhythmia episode to a useror process.

This section is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is an illustration of portions of a system that uses an IMD.

FIG. 2 is a flow chart of an example of a method of classifying adetected tachyarrhythmia.

FIGS. 3A and 3B show examples of electrograms sensed during atachyarrhythmia onset episode.

FIG. 4 is a block diagram of portions of an example of a device toclassify a detected tachyarrhythmia.

FIG. 5 shows a flow diagram of an example of a method for classifying atachyarrhythmia episode.

FIG. 6 shows a flow diagram of an example of a method that combinestachyarrhythmia detection enhancements.

FIG. 7 shows a flow diagram of another example of a method that combinestachyarrhythmia detection enhancements.

DETAILED DESCRIPTION

This document discusses systems and methods for improved detection ofcardiac events by an IMD. Specifically systems and methods for improveddiscrimination or classification of tachyarrhythmia by an IMD aredescribed.

An implantable medical device (IMD) may include one or more of thefeatures, structures, methods, or combinations thereof described herein.For example, a cardiac monitor or a cardiac stimulator may beimplemented to include one or more of the advantageous features orprocesses described below. It is intended that such a monitor,stimulator, or other implantable or partially implantable device neednot include all of the features described herein, but may be implementedto include selected features that provide for unique structures orfunctionality. Such a device may be implemented to provide a variety oftherapeutic or diagnostic functions.

FIG. 1 is an illustration of portions of a system 100 that uses an IMD105. Examples of the IMD 105 include, without limitation, a pacemaker, acardioverter, a defibrillator, a cardiac resynchronization therapy (CRT)device, and other cardiac monitoring and therapy delivery devices,including cardiac devices that include or work in coordination with oneor more neuro-stimulating devices, drugs, drug delivery systems, orother therapies. As one example, the system 100 shown can be used todetect and treat a cardiac arrhythmia such as tachyarrhythmia. The IMD105 typically includes an electronics unit coupled by one or morecardiac leads 110, 115, 125, to a heart of a patient or subject. Theelectronics unit of the IMD 105 typically includes components that areenclosed in a hermetically-sealed housing or “can.” System 100 alsotypically includes an IMD programmer or other external system 190 thatcommunicates one or more wireless signals 185 with the IMD 105, such asby using radio frequency (RF) or one or more other telemetry signals.

The example shown includes right atrial (RA) lead 110 having a proximalend 111 and a distal end 113. Proximal end 111 is coupled to a headerconnector 107 of the IMD 105. Distal end 113 is configured for placementin the RA in or near the atrial septum. RA lead 110 may include a pairof bipolar electrodes, such as an RA tip electrode 114A and an RA ringelectrode 114B. RA electrodes 114A and 114B are incorporated into thelead body at distal end 113 for placement in or near the atrial septum,and are each electrically coupled to IMD 105 through a conductorextending within the lead body. The RA lead is shown placed in or nearthe atrial septum, but the RA lead may be placed in the atrialappendage.

The example shown also includes right ventricular (RV) lead 115 having aproximal end 117 and a distal end 119. Proximal end 117 is coupled toheader connector 107. Distal end 119 is configured for placement in theRV. RV lead 115 may include one or more of a proximal defibrillationelectrode 116, a distal defibrillation electrode 118, an RV tipelectrode 120A, and an RV ring electrode 120B. Defibrillation electrode116 is incorporated into the lead body in a location suitable forsupraventricular placement in the RA or the superior vena cava.Defibrillation electrode 118 is incorporated into the lead body neardistal end 119 for placement in the RV. RV electrodes 120A and 120B mayform a bipolar electrode pair and are incorporated into the lead body atdistal end 119. Electrodes 116, 118, 120A, and 120B are eachelectrically coupled to IMD 105 through a conductor extending within thelead body. Proximal defibrillation electrode 116, distal defibrillationelectrode 118, and/or an electrode formed on the can of IMD 105 allowfor delivery of cardioversion/defibrillation pulses to the heart.

RV tip electrode 120A, RV ring electrode 120B, and/or an electrodeformed on the can of IMD 105 allow for sensing an RV electrogramindicative of RV depolarizations and delivering RV pacing pulses. Anycombination of RV tip electrode 120A, RV ring electrode 120B, and anelectrode formed on the can of IMD 105, or other ventricular electrodecan be referred to as a ventricular channel. RA tip electrode 114A, RAring electrode 114B, and/or an electrode formed on the can of IMD 105allow for sensing an RA electrogram indicative of RA depolarizations anddelivering RA pacing pulses. Any combination of RA tip electrode 114A,RA ring electrode 114B, electrode formed on the can of IMD 105, and/orother atrial electrode can be referred to as an atrial channel. Sensingchannels can also include defibrillation electrodes. Any combination ofelectrodes that includes the proximal defibrillation electrode 116, thedistal defibrillation electrode 118, and/or an electrode formed on thecan of the IMD 105 can be referred to as a shock channel.

Sensing and pacing allows the IMD 105 to adjust timing of the heartchamber contractions. In some device examples, IMD 105 can adjust thetiming of ventricular contractions with respect to the timing of atrialcontractions delay by sensing a contraction in the RA and pacing the RVat the desired atrial-ventricular (AV) delay time.

Also shown is a left ventricular (LV) lead 125. LV lead 125 is acoronary pacing and/or sensing lead that includes an elongate lead bodyhaving a proximal end 121 and a distal end 123. Proximal end 121 iscoupled to header connector 107. Distal end 123 is configured forplacement or insertion in the coronary vein. LV lead 125 may include anLV ring or tip electrode 128A and an LV ring electrode 128B. The distalportion of LV lead 125 is configured for placement in the coronary sinusand coronary vein such that LV electrodes 128A and 128B are placed inthe coronary vein. LV electrodes 128A and 128B may form a bipolarelectrode pair and are incorporated into the lead body at distal end 123and each electrically coupled to IMD 105 through a conductor extendingwithin the lead body. LV tip electrode 128A, LV ring electrode 128B,and/or an electrode formed on the can of IMD 105 allow for sensing an LVelectrogram indicative of LV depolarizations and delivering LV pacingpulses. Any combination of LV tip electrode 128A, LV ring electrode128B, and/or electrode formed on the can of IMD 105, and/or otherventricular electrode can also be referred to as a ventricular channel.

Other forms of electrodes include meshes and patches, which may beapplied to one or more portions of heart, or which may be implanted inone or more other areas of the body to help “steer” electrical currentproduced by IMD 105 in FIG. 1. The IMDs may be configured with a varietyof electrode arrangements, including transvenous, endocardial, orepicardial electrodes (e.g., intrathoracic electrodes), or subcutaneous,non-intrathoracic electrodes, such as can, header, or indifferentelectrodes, or subcutaneous array or lead electrodes (e.g.,non-intrathoracic electrodes). Monitoring of electrical signals relatedto cardiac activity may provide early, if not immediate, diagnosis ofcardiac disease.

Typically, cardioverter defibrillators detect tachyarrhythmia by firstdetecting a rapid heart rate. Detection enhancements are sometime usedto further distinguish or classify the detected arrhythmia. A detectionenhancement example includes determining whether the rate detected in aventricle (V Rate) is greater than the rate detected in an atrium (ARate) by a specified rate threshold (e.g., V Rate>A Rate by more thanten beats per minute, or 10 bpm). This is often an indication that thearrhythmia is VT. However, sometimes the enhancements fail to accuratelydistinguish VT from SVT, especially during a tachyarrhythmia episodewhen ventricular events occur about one-to-one with atrial events duringthe tachyarrhythmia episode.

To improve classification of detected tachyarrhythmia, determiningwhether events in an atrium are “driving” events sensed in a ventricleor whether events in a ventricle are driving events sensed in an atriumcan improve detection and discrimination of tachyarrhythmia.

FIG. 2 is a flow chart of an example of a method 200 of classifying adetected tachyarrhythmia. At block 205, cardiac depolarization intervalsare monitored in an atrium and in a ventricle of a heart of a subjectusing an IMD.

At block 210, an episode of tachyarrhythmia is detected using the IMD.In some examples, the episode is detected when a ventriculardepolarization rate is detected that exceeds a specified lowesttachyarrhythmia detection rate. In some examples, the episode isdetected when a specified number of sensed ventricular depolarizationintervals are less than a specified tachyarrhythmia detection thresholdinterval value. In some examples, detection parameters are specified byprogramming the parameters into the device.

At block 215, it is determined whether the relationship of sensed atrialdepolarizations to sensed ventricular depolarizations is substantiallyone-to-one during the episode. In some examples, ventricular events aredeemed to occur substantially one-to-one with atrial events during theepisode when the number of ventricular depolarizations differs from thenumber of atrial depolarizations by less than a specified thresholddepolarization difference value (e.g., 2 or less) during thetachyarrhythmia episode. Stated another way, the episode is deemed to bea one-to-one episode when for almost every atrial event there is aventricular event and for almost every ventricular event there is anatrial event. In some examples, ventricular events are deemed to occursubstantially one-to-one with atrial events during a tachyarrhythmiaepisode when the detected ventricular rate differs from the detectedatrial rate by less than a specified rate difference (e.g., 10 bpm). Insome examples, ventricular events are deemed to occur substantiallyone-to-one with atrial events during the tachyarrhythmia episode whenmeasured ventricular-to-ventricular (V-V) intervals differ from measuredatrial-to-atrial (A-A) intervals by less than a specified thresholdinterval value during the onset episode.

At block 220, the A-A intervals and the V-V intervals are monitoredduring the episode to determine if there is any change in the intervals.In particular, the monitoring looks for a change in one or both of anA-A interval and a V-V interval that exceeds a specified thresholdinterval change value (e.g., 20 milliseconds, or ms). If there is achange, it is determined whether the change is a shortening or aprolonging from the previous intervals and it is determined which heartchamber first experienced the change in depolarization intervals. Theepisode is then classified using the information about the change.

The episode is classified as VT when detecting one of a shortening orprolonging of an A-A interval during the episode, and the A-A intervalshortening or prolonging is immediately preceded by substantially thesame shortening or prolonging of a V-V interval. In some examples, thechange is determined to be substantially the same between the twochambers when a measured difference between the V-V interval and the A-Ainterval is less than a specified threshold interval difference value.In certain examples, the threshold interval difference value is 20 ms.In certain examples, the threshold interval difference value is 50 ms.

In some examples, the episode is classified as supra-ventriculartachycardia (SVT) when the measured V-V interval change during theepisode is immediately preceded by the A-A interval change and thedifference between the A-A interval change and the V-V interval changeis less than the specified interval change threshold value. In someexamples, shortening or prolonging of more than one A-A and V-V intervalis required before the episode is classified as SVT or VT.

FIGS. 3A and 3B show examples of electrograms sensed during atachyarrhythmia onset episode. In FIG. 3A, the top trace 305 is anelectrogram sensed using an atrial channel. The middle trace 310 is anelectrogram sensed using a ventricular channel, and the bottom trace 315is an electrogram sensed using a shock channel. The electrograms show anexample of depolarization interval shortening (320, 325). FIG. 3B showsan example of depolarization interval prolongation (330, 335). Note thatthe depolarizations in the atrium occur one-to-one with thedepolarizations in the ventricle. In FIG. 3A, because the shortening 320in the atrium precedes the shortening 325 in the ventricle and becausethe shortening is substantially the same in the intervals, the episodeis classified as SVT. Similarly, in FIG. 3B, because the prolonging 330in the atrium precedes the prolonging 335 in the ventricle and becausethe prolonging is substantially the same in the intervals, the episodeis also classified as SVT.

In some examples, when the V-V intervals and the A-A intervals do notchange during the episode, or do not change for specified duration oftime or heartbeats, the episode may be classified as sinus tachycardia(ST). In some examples, if there is no detected difference between theV-V interval durations and the A-A interval durations during thetachyarrhythmia episode, or the detected difference is less than thespecified interval change threshold value, the episode is classified asST. In some examples, when the episode is initially classified as ST,other detection enhancements are activated to confirm ST.

Returning to FIG. 2 at block 225, the classification of thetachyarrhythmia episode is provided to a user or process. The processmay be executing on a processor such as a microprocessor. Theclassification may be used to initiate or inhibit delivery ofanti-tachyarrhythmia therapy, or the classification may be communicatedto a process executing on a second device.

FIG. 4 is a block diagram of portions of an example of a device 400 toclassify a detected tachyarrhythmia. The device 400 includes animplantable cardiac signal sensing circuit 405. The cardiac signalsensing circuit 405 provides a sensed depolarization signal from aventricle and a sensed depolarization signal from an atrium whenattached to appropriate electrodes.

The device 400 also includes a controller circuit 410 communicativelycoupled to the cardiac signal sensing circuit 405. The communicativecoupling allows electrical signals to be communicated between thecardiac signal sensing circuit 405 and the controller circuit 410 eventhough there may be intervening circuitry.

The controller circuit 410 may include a processor such as amicroprocessor, a digital signal processor, application specificintegrated circuit (ASIC), microprocessor, or other type of processor,interpreting or executing instructions in software or firmware. Thecontroller circuit 410 includes other circuits or sub-circuits toperform the functions described. These circuits may include software,hardware, firmware or any combination thereof. Multiple functions can beperformed in one or more of the circuits as desired.

The controller circuit 410 includes a one-to-one detector circuit 415.The one-to-one detector circuit 415 determines whether a relationship ofatrial depolarizations to ventricular depolarizations is substantiallyone-to-one. In some examples, the one-to-one detector circuit 415measures sensed cardiac depolarization intervals of the atrium and theventricle. In certain examples, the one-to-one detector indicates (e.g.,generates a signal) that ventricular events occur about one-to-one withatrial events when measured V-V intervals differ from measured A-Aintervals by less than a specified threshold interval value.

In some examples, the one-to-one detector monitors (e.g., counts) atrialand ventricular depolarizations during the episode and indicates thatventricular events occur substantially one-to-one with atrial eventswhen the number of ventricular depolarizations differs from the numberof atrial depolarizations by less than a specified thresholddepolarization difference value. In some examples, the one-to-onedetector determines depolarization rate for the atrium and theventricle, and indicates that the ventricular events occur one-to-onewith atrial events when the detected ventricular rate differs from thedetected atrial rate by less than a specified rate difference.

The determination of whether an episode is one-to-one may be complicatedby the occurrence of premature ventricular contractions (PVCs) andpremature atrial contractions (PACs). Typically, the one-to-one detectorcircuit 415 deems that the relationship of depolarizations issubstantially one-to-one during the episode when the difference betweenthe number of atrial depolarizations and the number of ventriculardepolarizations is less than a first specified threshold depolarizationdifference value (e.g., 1 or 2 depolarizations). To allow for PVCs, theone-to-one detector circuit 415 deems that the relationship ofdepolarizations is substantially one-to-one when the number ofventricular depolarizations is more than a number of detected atrialdepolarizations but is less than a second specified thresholddepolarization difference value (e.g., 3 or 4 depolarizations).Similarly, to allow for PACs, in some examples the one-to-one detectorcircuit 415 deems that the relationship of depolarizations issubstantially one-to-one when the number of atrial depolarizations ismore than a number of detected ventricular depolarizations but is lessthan a second specified threshold depolarization difference value.

Far-field sensing of events may also complicate the one-to-onedetermination. Far-field sensing refers to sensing events in a firstchamber (e.g., an atrium) that are actually occurring in a secondchamber (e.g., a ventricle). Typically, IMDs ignore a depolarizationduring a device-specified refractory period to avoid cross chambersensing. However, these depolarizations may be important to a one-to-onedetermination.

In some examples, the cardiac signal sensing circuit 405 senses adepolarization during the device-specified refractory period. Theone-to-one detector circuit 415 includes the depolarization in theone-to-one determination unless determining that the senseddepolarization is a far-field sensed event, in which case the event isignored. In certain examples, the one-to-one detector circuit 415determines that a depolarization sensed during the refractory period isfar-field when the amplitude of the sensed signal is less than aspecified threshold signal amplitude value. In certain examples, theone-to-one detector circuit 415 determines that a depolarization sensedduring the refractory period is far-field when the amplitude of thesensed signal is less than other sensed depolarization amplitudes bymore than a specified threshold difference value.

The controller circuit 410 also includes a tachyarrhythmiadiscrimination circuit 420 to detect an episode of tachyarrhythmia. Insome examples, the tachyarrhythmia discrimination circuit 420 detectsthe episode when a determined depolarization rate or interval satisfiesa lowest tachyarrhythmia detection threshold rate or longest detectioninterval. The tachyarrhythmia discrimination circuit 420 uses detectedchanges in A-A intervals and V-V intervals during the one-to-one episodeto classify the tachyarrhythmia. The tachyarrhythmia discriminationcircuit 420 may bypass or cancel the one-to-one monitoring when adetermined depolarization rate or interval satisfies a ventricularfibrillation detection threshold rate or interval.

When the one-to-one detector circuit 415 indicates that the relationshipatrial depolarizations to ventricular depolarizations is substantiallyone-to-one during the tachyarrhythmia episode, the tachyarrhythmiadiscrimination circuit 420 classifies the episode as VT when detectingone of a shortening or a prolonging of an A-A interval during theepisode that is immediately preceded by the same one of a shortening orprolonging of a V-V interval.

The tachyarrhythmia discrimination circuit 420 classifies the episode assupra-ventricular tachycardia (SVT) when the episode is indicated to beone-to-one and when detecting one of a shortening or prolonging of a V-Vinterval during the episode that is immediately preceded by the same oneof a shortening or prolonging of an A-A interval. As explainedpreviously, in some examples shortening or prolonging of more than oneA-A and V-V interval is required before the episode is classified as SVTor VT.

In some examples, the controller circuit 410 includes an interval changecircuit 445 for detecting changes in intervals. In some examples, theinterval change circuit 445 calculates a difference between consecutiveintervals in the atrium and in the ventricle. The interval changecircuit indicates a change in A-A or V-V intervals when the measuredchange exceeds a specified threshold change value (e.g., 20 ms). Theinterval change circuit 445 may indicate that the change is shorteningor prolonging based on whether the calculated difference is a positiveor negative quantity.

For instance, the interval change circuit 445 may subtract a currentinterval from the previous interval. If the magnitude of the calculatedinterval change between the current interval and the previous intervalexceeds the threshold value, and the sign of the calculated differenceis negative, the interval change included a prolonging of the intervals.If the sign of the calculated difference is positive, the intervalchange included a shortening of the intervals. In some examples, theinterval change circuit 445 calculates a net interval change over Ndepolarization intervals, where N is an integer (e.g., 3). The intervalchange circuit declares a change in the depolarization intervals whenthe measured total net interval change exceeds the specified thresholdchange value.

According to some examples, the controller circuit 410 includes a firstcounter circuit 425 and a second counter circuit 430. Thetachyarrhythmia discrimination circuit 420 is configured to incrementthe first counter 425 when the detected shortening or prolonging of theA-A interval immediately precedes the detected shortening or prolongingof the V-V interval during the episode. This can be thought of ascreating a count of SVT indicated events during the episode. This isshown in blocks 510 and 515 of the flow chart in FIG. 5.

The tachyarrhythmia discrimination circuit 420 increments the secondcounter when the detected shortening or prolonging of the V-V intervalimmediately precedes the detected shortening or prolonging of the A-Ainterval during the episode. This can be thought of as creating a countof VT indicated events during the episode. In some examples, thetachyarrhythmia discrimination circuit 420 also requires that theinterval from a ventricular depolarization to an atrial depolarization(V-A) interval is greater than a specified threshold V-A interval value(e.g., 100 ms) to increment the second count. This is shown in blocks520 and 525 of the flow chart of FIG. 5.

The tachyarrhythmia discrimination circuit 420 classifies the episode asSVT when a count of the first counter 425 exceeds a count of the secondcounter 430 by a specified threshold count value. For example, as shownin FIG. 5 at blocks 530 and 535, the episode may be classified as SVTwhen the first counter exceeds the second counter by two counts. Thetachyarrhythmia discrimination circuit 420 classifies the episode as VTwhen the count of the second counter 430 is higher than the count of thefirst counter 425 by the specified threshold count. For example, asshown in FIG. 5 at blocks 540 and 545, the episode may be classified asSVT when the second counter exceeds the first counter by two counts.

At block 550 of FIG. 5, if no variation in cardiac cycle length isdetected, the classification of the episode may be indeterminate. Insome examples, if no variation in cardiac cycle length is detected inthe episode, tachyarrhythmia discrimination circuit 420 may classify theepisode as ST. In some examples, if the detected difference between theV-V interval durations and the A-A interval durations during thetachyarrhythmia episode is less than the specified interval changethreshold value, the episode is classified as ST. In some examples, whenthe episode is classified as ST, other detection enhancements areactivated to confirm ST.

In some examples, the device includes a memory circuit 440 integral toor communicatively coupled to the controller circuit 410. A segment of asignal sensed from the ventricle (e.g., a signal sensed over ten secondstime) and a segment of a signal sensed from the atrium may be stored ina buffer in the memory circuit 440. The signal segments stored in thebuffer are used by the one-to-one detector circuit 415 and thetachyarrhythmia discrimination circuit 20 to classify thetachyarrhythmia episode.

In some examples, the one-to-one detector circuit 415 monitors cardiacdepolarization intervals as they occur in real time and thetachyarrhythmia discrimination circuit 420 classifies the episode inreal time. The one-to-one detector circuit 415 may continue themonitoring while the relationship is determined to be substantiallyone-to-one and a difference between the count of the first counter andthe count of the second counter is less than the specified thresholdcount.

According to some examples, the one-to-one monitoring continues untilanother indication of tachyarrhythmia occurs, such as when the episodeis no longer substantially one-to-one. In some examples, the one-to-onemonitoring continues until the detected ventricular rate exceeds theatrial rate by more than a threshold rate value (e.g., more than 10bpm). In this case the tachyarrhythmia discrimination circuit 420 mayclassify the detected episode as VT. In some examples, the one-to-onemonitoring continues until the detected atrial rate exceeds theventricular rate by more than a threshold rate value. In this case thetachyarrhythmia discrimination circuit 420 may classify the detectedepisode as atrial tachyarrhythmia. In some examples, the one-to-onedetection continues until the detected episode self-terminates.

In some examples, the controller circuit 410 is configured to initiatestorage of at least one of electrograms and markers when at least one ofthe relationship is determined to be different than substantiallyone-to-one, or the relationship is determined to be substantiallyone-to-one and the episode is classified, such as when the differencebetween the count of the first counter and the count of the secondcounter exceeds the specified threshold count.

When the episode is classified, the tachyarrhythmia discriminationcircuit 420 provides the classification of the tachyarrhythmia episodeto a user or process. In some examples, the device 400 includes atherapy circuit 435 to provide one or more of anti-tachyarrhythmiapacing (ATP) therapy or high-energy defibrillation/cardioversion shocktherapy to the subject. In some examples, the device 400 includes aswitch circuit (not shown) to disconnect the cardiac signal sensingcircuit 405 from one or more electrodes during delivery of the therapyto protect the sensing circuitry.

The tachyarrhythmia discrimination circuit 420 may provide theclassification to a process executing on the controller circuit 410. Thecontroller circuit 410 may initiate at least one of cardioversion shocktherapy, defibrillation shock therapy, and ATP therapy, when the episodeis classified as VT. The controller circuit 410 may inhibit therapy ordelay therapy if the episode is classified as SVT or ST, such as whenthe A-A depolarization interval durations and the V-V interval durationsremain unchanged during the episode.

In some examples, the device 400 includes a communication circuit 450 Insome examples, the process is executing on a remote device. The medicaldevice 400 may include a communication circuit 450 to wirelesslycommunicate information with the remote device. An approach tocommunications using an IMD can be found in U.S. Pat. No. 7,664,553,“Systems and Method for Enabling Communications with Implantable MedicalDevices,” filed Apr. 27, 2005, which is incorporated herein by referencein its entirety.

In some examples, the device 400 communicates a tachyarrhythmiaclassification to a remote device that includes an IMD programmer. Insome examples, the device 400 communicates with the remote device via athird device (e.g., a repeater). In some examples, the remote device ispart of an advanced patient management (APM) system, and includes aserver connected to a computer network such as the internet for example.

The method of determining whether events in one chamber are driving orinfluencing the events in the other chamber can be combined with othertachyarrhythmia detection enhancements. In some examples,tachyarrhythmia discrimination circuit 420 detects tachyarrhythmia whenthe ventricular heart rate exceeds the atrial heart rate (V Rate>ARate). The tachyarrhythmia discrimination circuit 420 may recurrentlyupdate an average ventricular contraction interval (V-V interval) anddetects a tachyarrhythmia when the average ventricular depolarizationrate exceeds an average atrial depolarization rate by more than aspecified rate threshold value. Descriptions of systems and methods forclassifying detected tachycardia based on average atrial and ventricularrates calculated from selected atrial and ventricular intervals is foundin co-pending U.S. patent application Ser. No. 11/054,726, Elahi et al.,entitled, “Method and Apparatus for Rate Accuracy Enhancement inVentricular Tachycardia Detection,” filed Feb. 10, 2005, which isincorporated herein by reference in its entirety.

In another detection enhancement, the tachyarrhythmia discriminationcircuit 420 performs a morphology comparison of a sensed cardiac signalto a template of a known morphology (such as normal sinus rhythm) storedin memory. The tachyarrhythmia discrimination circuit 420 can calculatea coefficient of correlation (e.g., a feature correlation coefficient orFCC) that is a measure of similarity between the sensed cardiac signaland the template. If the correlation coefficient indicates a high degreeof similarity between the sensed cardiac signal and the template, thesensed rhythm is more likely to be supraventricular rhythm. Forinstance, if the calculated value of correlation exceeds a specifiedcorrelation threshold value, the tachyarrhythmia discrimination circuit420 classifies an onset episode as SVT.

Examples of methods to discriminate heart rhythms using analysis of themorphology of sensed cardiac signal can be found in Schwartz at al.,“Cardiac Rhythm Management Systems and Methods Using Multiple MorphologyTemplates for Discriminating Between Rhythms,” U.S. Pat. No. 7,031,764,filed Nov. 8, 2002 which is incorporated herein by reference in itsentirety.

In another example, a template can be generated from a snapshotrepresentative of one of the patient's normal supra-ventricularconducted beats. Cardiac signals are sensed from pacing leads (ratechannel) and shock leads (shock channel). A fiducial point is determinedfrom the signals sensed on the rate channels and is used to alignsignals sensed on the shock channels. A template for a patient isgenerated using the aligned shock channel signals. The template isrepresentative of one of the patient's normal supra-ventricularconducted beats. Subsequently detected beats are then used to confirmthat the generated template is representative of one of the patient'snormal supra-ventricular conducted beats. Systems and methods forgenerating templates using a snapshot of the patient's normalsupra-ventricular conducted beats are described in Kim et al., U.S. Pat.No. 6,708,058, entitled “Normal Cardiac Rhythm Template GenerationSystem and Method,” filed Apr. 30, 2001, which is incorporated herein byreference in its entirety.

In another example, a template of a patient's supraventricular rhythm isgenerated from characterizations performed while the heart is beingpaced. During the characterization, various pacing parameters aremodified and the patient's supraventricular rhythm is characterizedwhile the pacing parameters are modified. Systems and methods forgenerating a template to represent a patient's supraventricular rhythmare described in Bocek et al., U.S. Pat. No. 6,889,079, entitled “Methodand System for Characterizing Supraventricular Rhythm During CardiacPacing,” filed Apr. 12, 2002, which is incorporated herein by referencein its entirety.

Another tachyarrhythmia detection enhancement is rate stability. In someexamples, the tachyarrhythmia discrimination circuit 420 uses anassessment of heart rhythm stability to classify the arrhythmia when asudden increase in heart rate is detected. Stability in the rhythm witha sudden onset tends to indicate VT while less stability or a moregradual onset may indicate SVT. Examples of methods and systems todetect arrhythmia and assess the stability of the rhythms are found inGilkerson et al., U.S. Pat. No. 6,493,579, entitled “System and Methodfor Detection Enhancement Programming,” filed Aug. 20, 1999, which isincorporated herein by reference in its entirety.

Another tachyarrhythmia detection enhancement is sustained rate duration(SRD). In some examples, three rate zones are used as a first tierclassification of a detected arrhythmia rate into a slow tachycardia(VT-1) zone (e.g., 170-199 bpm, a VT zone (e.g., 200-249 bpm), and a VFzone (e.g., over 250 bpm). The rate zones can be programmable. In SRDdetection, the detected rate has to remain in that tachyarrhythmiadetection rate zone for a specified duration (e.g., either in seconds orheart beats) to be classified as that type of tachyarrhythmia.

FIG. 6 shows a flow diagram of an example of a method 600 that combinestachyarrhythmia detection enhancements. At block 605, an episode oftachyarrhythmia is detected by the tachyarrhythmia discriminationcircuit 420. At block 610, the one-to-one detector circuit 415determines if the episode is substantially one-to-one. If the episode isnot substantially one-to-one, the tachyarrhythmia discrimination circuit420 determines if the V Rate exceeds the A Rate by more than a thresholdrate value at block 615. If V Rate does exceed the A Rate by thethreshold amount, the tachyarrhythmia discrimination circuit 420classifies the episode as VT at block 620.

At block 625, if the episode is substantially one-to-one, thetachyarrhythmia discrimination circuit 420 determines if any detectedchange in the intervals happens in the atrium first. If a detectedchange occurs and it occurs in the atrium first, the tachyarrhythmiadiscrimination circuit 420 classifies the episode as SVT at block 630.At block 635, if a detected change occurs, it occurs in the ventriclefirst, and the V-A interval is greater than a specified threshold value,the tachyarrhythmia discrimination circuit 420 classifies the episode asVT at block 645. If no change in the intervals during the one-to-oneepisode occurs after a specified period of time, the tachyarrhythmiadiscrimination circuit 420 may apply further enhanced detection methodsto classify the tachyarrhythmia.

At block 640, the tachyarrhythmia discrimination circuit 420 performs amorphology comparison of a sensed cardiac signal to a template. Themorphology comparison may include calculation of an FCC, and the storedtemplate may be a representation of NSR. The tachyarrhythmiadiscrimination circuit 420 determines whether the FCC satisfies aspecified FCC threshold (e.g., FCC≧0.94) for a specified number of Xbeats out of Y beats (e.g., 3 out of 10 beats). If the sensed cardiacsignal sufficiently compares to the template of NSR, the tachyarrhythmiadiscrimination circuit 420 classifies the episode as SVT at block 650.If the conditions of block 640 are not satisfied, the method continuesto block 655.

At block 655, the tachyarrhythmia discrimination circuit 420 determinesa measure of stability of the ventricular rate. In some examples, if thevariation in sensed ventricular depolarizations exceeds a thresholdvariation threshold value and the atrial rate exceeds a specified atrialrate threshold, the tachyarrhythmia discrimination circuit 420classifies the episode as SVT at block 660. If the conditions of block655 are not satisfied, the tachyarrhythmia discrimination circuit 420classifies the episode as VT at block 665.

The decision blocks on the right of the flow diagram that include VRate>A Rate, calculate FCC, and determine if V Rate is stable while theA Rate is high can be included in a method of detection referred to asRhythm ID™. The decision blocks to the left show how one-to-onedetection and heart chamber drive can be incorporated into Rhythm ID™.

FIG. 7 shows a flow diagram of another example of a method 700 thatcombines tachyarrhythmia detection enhancements. At block 705, anepisode of tachyarrhythmia is detected by the tachyarrhythmiadiscrimination circuit 420. At block 710, the one-to-one detectorcircuit 415 determines if the episode is substantially one-to-one. Ifthe episode is not substantially one-to-one, the tachyarrhythmiadiscrimination circuit 420 determines if the V Rate exceeds the A Rateby more than a threshold rate value at block 715. If V Rate does exceedthe A Rate by the threshold amount, the tachyarrhythmia discriminationcircuit 420 classifies the episode as VT at block 720.

At block 725, if the episode is substantially one-to-one, thetachyarrhythmia discrimination circuit 420 determines if any detectedchange in the intervals happens in the atrium first. If a detectedchange occurs and it occurs in the atrium first, the tachyarrhythmiadiscrimination circuit 420 classifies the episode as SVT at block 730.At block 735, if a detected change occurs, it occurs in the ventriclefirst, and the V-A interval is greater than a specified threshold value,the tachyarrhythmia discrimination circuit 420 classifies the episode asVT at block 745. If no change in the intervals during the one-to-oneepisode occurs after a specified period of time, the tachyarrhythmiadiscrimination circuit 420 may apply further enhanced detection methodsto classify the tachyarrhythmia.

At block 740, the tachyarrhythmia discrimination circuit 420 determinesa measure of stability of V-V intervals. In some examples, thetachyarrhythmia discrimination circuit 420 measures the differencesbetween V-V intervals. If the V-V intervals are stable then the V-Vintervals are uniform and the differences will approach zero. If the V-Vintervals are unstable, then the calculated differences will be greaterthan zero. If the measured differences indicate that the rhythm duringthe detected episode is unstable, the tachyarrhythmia discriminationcircuit 420 classifies the episode as SVT at block 750. If thetachyarrhythmia discrimination circuit 420 determines that the rhythm isstable, the method continues at block 755.

At block 755, if the measured differences indicate that the rhythmduring the detected episode is stable and the tachyarrhythmiadiscrimination circuit 420 determined that an increase in heart rate wasgradual rather than sudden, the method proceeds to block 760. At block760, if the A rate is less than a specified atrial fibrillationdetection rate threshold, the tachyarrhythmia discrimination circuit 420classifies the episode as SVT at block 765. If the A rate is greaterthan or equal to the atrial fibrillation detection rate threshold, thetachyarrhythmia discrimination circuit 420 classifies the episode as VTat block 770.

At block 775, if the measured differences indicate that the rhythmduring the detected episode is stable and the tachyarrhythmiadiscrimination circuit 420 determined that an increase in heart rate wassudden rather than gradual, the tachyarrhythmia discrimination circuit420 classifies the episode as VT at block 770.

The decision blocks on the right of the flow diagram that include VRate>A Rate, the stability determinations, and A Rate<AFib can beincluded in a method of detection referred to as Onset/Stability™. Thedecision blocks to the left show how one-to-one detection and heartchamber drive can be incorporated into Onset/Stability™.

Table 1 shows how the detection enhancements can be used with ratedetection zones. The rate detection zones can be programmable. The firstrow of the Table shows how rhythm enhancements can be combined inclassifying tachyarrhythmia when three rate zones of VT-1, VT, and VFare used. The Table shows that Rhythm ID™, Onset/Stability™, V Rate>ARate, SRD, an AFib detection threshold rate, and one-to-one detectionwith AV drive can be used with detected rates in the VT-1 and VT zones.When the VF rate is detected, the device 400 proceeds to provide therapywithout any classification enhancements.

In the second row of the Table, the VT-1 zone is designated as amonitor-only zone. Arrhythmias with rates in monitor-only zone may onlycause storage of electrograms to be initiated. In the third row of theTable, only two detection zones VT and VF are used.

When a tachyarrhythmia episode is detected, determining if the episodeis one-to-one and monitoring the heart chambers for a change thatindicates which chamber is during the tachyarrhythmia can be usefulalone in classifying tachyarrhythmia, or can be useful when combinedwith other tachyarrhythmia detection enhancements.

TABLE 1 VT-1 Zone VT Zone VF Zone 3-zone Rhythm ID ™ Rhythm ID ™ Noneconfiguration Onset/Stability ™ Onset/Stability ™ V > A, SRD, V > A,SRD, AFib Rate Threshold AFib Rate Threshold One-One detection andOne-One detection and AV Drive AV Drive 3-zone None Rhythm ID ™ Noneconfiguration Onset/Stability (with V > A, SRD, Monitor AFib RateThreshold Only zone) One-One detection and AV Drive 2-zone configurationRhythm ID ™ None Onset/Stability V > A, SRD, AFib Rate Threshold One-Onedetection and AV Drive

CONCLUSION

Systems and methods for improved discrimination or classification oftachyarrhythmia by a CRM device are described herein.

Example 1 includes subject matter (such as an apparatus) comprising animplantable cardiac signal sensing circuit, configured to provide asensed depolarization signal from a ventricle and a senseddepolarization signal from an atrium, and a controller circuitcommunicatively coupled to the implantable cardiac signal sensingcircuit. The controller circuit includes a one-to-one detector circuitand a tachyarrhythmia discrimination circuit. The one-to-one detectorcircuit is configured to measure cardiac depolarization intervals of theatrium and the ventricle and determine whether a relationship of atrialdepolarizations to ventricular depolarizations is substantiallyone-to-one. The tachyarrhythmia discrimination circuit is configured todetect an episode of tachyarrhythmia while the relationship atrialdepolarizations to ventricular depolarizations is substantiallyone-to-one, classify the episode as ventricular tachycardia (VT) whendetecting one of a shortening or prolonging of an A-A interval duringthe episode that is immediately preceded by the same one of a shorteningor prolonging of a V-V interval, and provide the classification of thetachyarrhythmia episode to a user or process.

In Example 2, the tachyarrhythmia discrimination circuit of Example 1 isoptionally configured to classify the episode as supra-ventriculartachycardia (SVT) when detecting one of a shortening or prolonging of aV-V interval during the episode that is immediately preceded by the sameone of a shortening or prolonging of an A-A interval.

In Example 3, the controller circuit of one or any combination ofExamples 1 and 2 optionally includes a first counter circuit and asecond counter circuit. The tachyarrhythmia discrimination circuit isoptionally configured to increment the first counter when the detectedshortening or prolonging of the A-A interval immediately precedes thedetected shortening or prolonging of the V-V interval during theepisode, increment the second counter when the detected shortening orprolonging of the V-V interval immediately precedes the detectedshortening or prolonging of the A-A interval during the episode and aninterval from a ventricular depolarization to an atrial depolarization(V-A) is greater than a specified threshold V-A interval value, classifythe episode as SVT when a count of the first counter exceeds a count ofthe second counter by a specified threshold count, and classify theepisode as VT when the count of the second counter exceeds the count ofthe first counter by the specified threshold count.

In Example 4, the one-to-one detector circuit of one or any combinationof Examples 1-3 is optionally configured to monitor cardiacdepolarization intervals as they occur in real time, and continue themonitoring while the relationship is determined to be substantiallyone-to-one and a difference between the count of the first counter andthe count of the second counter is less than the specified thresholdcount. The controller circuit is optionally configured to initiatestorage of at least one of an electrogram and a marker when at least oneof the relationship is determined to be different than substantiallyone-to-one or the relationship is determined to be substantiallyone-to-one and the difference between the count of the first counter andthe count of the second counter exceeds the specified threshold count.

In Example 5, the one-to-one detector circuit of one or any combinationof Examples 1-4 is optionally configured to deem that the relationshipof atrial depolarizations to ventricular depolarizations issubstantially one-to-one when the difference between a number of atrialdepolarizations and a number of ventricular depolarizations during theepisode is less than a specified threshold depolarization differencevalue.

In Example 6, the cardiac signal sensing circuit of one or anycombination of Examples 1-5 is optionally configured to sense adepolarization during a device-specified refractory period, and whereinthe one-to-one detector circuit is configured to include thedepolarization in the one-to-one determination unless determining thatthe sensed depolarization is a far-field sensed event.

In Example 7, the one-to-one detector circuit of one or any combinationof Examples 1-6 is optionally configured to deem that the relationshipof depolarizations is substantially one-to-one during the episode whenthe number of atrial depolarizations is more than a number of detectedventricular depolarizations but is less than first specified thresholddepolarization difference value and the number of ventriculardepolarizations is more than a number of detected atrial depolarizationsbut is less than a second specified threshold depolarization differencevalue.

In Example 8, the tachyarrhythmia discrimination circuit of one or anycombination of Examples 1-7 is optionally configured to cancelone-to-one monitoring when detecting a depolarization rate ordepolarization interval that satisfies a ventricular fibrillation (VF)detection rate threshold or VF detection interval threshold.

In Example 9, the tachyarrhythmia discrimination circuit of one or anycombination of Examples 1-8 is optionally configured to detect atachyarrhythmia episode when a determined depolarization rate orinterval satisfies a lowest tachyarrhythmia detection threshold rate orinterval.

In Example 10, the subject matter of any or any combination of Examples1-9 optionally includes a therapy circuit communicatively coupled to thecontroller circuit and configured to provide at least one ofcardioversion shock therapy, defibrillation shock therapy, andanti-tachyarrhythmia pacing (ATP) therapy, and the controller circuit isoptionally configured to delay delivery of anti-tachyarrhythmia therapywhen A-A depolarization interval durations and V-V interval durationsremain unchanged during the episode.

Example 11 can include subject matter, or can optionally be combinedwith the subject matter of one or any combination of Examples 1-10 toinclude subject matter (such as a method, a means for performing acts,or a machine-readable medium including instructions that, when performedby the machine, cause the machine to perform acts), comprisingmonitoring cardiac depolarization intervals in an atrium and in aventricle of a heart of a subject using an implantable medical device(IMD), detecting an episode of tachyarrhythmia using the IMD,determining that a relationship of atrial (A-A) depolarizations toventricular (V-V) depolarizations is substantially one-to-one during theepisode, classifying the episode as ventricular tachycardia (VT) whendetecting one of a shortening or prolonging of an A-A interval duringthe episode that is immediately preceded by the same one of a shorteningor prolonging of a V-V interval, and providing the classification of thetachyarrhythmia episode to a user or process.

In Example 12, the subject matter of Example 11 optionally includesclassifying the episode as supra-ventricular tachycardia (SVT) whendetecting one of a shortening or prolonging of a V-V interval during theepisode that is immediately preceded by the same one of a shortening orprolonging of an A-A interval.

In Example 13, the subject matter of one or any combination of Examples11 and 12 optionally includes incrementing a first counter when thedetected shortening or prolonging of the A-A interval immediatelyprecedes the detected shortening or prolonging of the V-V intervalduring the episode, and incrementing a second counter when the detectedshortening or prolonging of the V-V interval immediately precedes thedetected shortening or prolonging of the A-A interval during the episodeand an interval from a ventricular depolarization to an atrialdepolarization (V-A) is greater than a specified threshold V-A intervalvalue, wherein classifying the episode as VT optionally includesclassifying the episode as VT when the count of the second counter ishigher than the count of the first counter by a specified thresholdcount, and wherein classifying the episode as SVT optionally includesclassifying the episode as SVT when a count of the first counter ishigher than a count of the second counter by the specified thresholdcount.

In Example 14, the subject matter of one or any combination of Examples11-13 optionally includes monitoring cardiac depolarization intervals asthey occur in real time, continuing the monitoring while therelationship is determined to be substantially one-to-one and adifference between counts of the first counter circuit and the secondcounter circuit is less than the specified threshold count, andinitiating storage of at least one of an electrogram and a marker whenat least one of the relationship is determined to be different thansubstantially one-to-one or the relationship is determined to besubstantially one-to-one and the difference between the count of thefirst counter and the count of the second counter satisfies thespecified threshold count.

In Example 15, the determining a relationship of atrial depolarizationsto ventricular depolarizations of one or any combination of Examples11-14 optionally includes deeming that the relationship is substantiallyone-to-one when the difference between a number of atrialdepolarizations and a number of ventricular depolarizations during theepisode is less than a specified threshold depolarization differencevalue.

In Example 16, the subject matter of one or any combination of examples11-15 optionally includes sensing a depolarization during a devicerefractory period; and including the depolarization in the one-to-onedetermination unless determining that the sensed depolarization is afar-field sensed event.

In Example 17, the deeming that the relationship is substantiallyone-to-one of one or any combination of Examples 11-16 optionallyincludes deeming that the relationship is substantially one-to-one whenthe number of atrial depolarizations is more than the number ofventricular depolarizations but is less than a first specified thresholddepolarization difference value, and deeming that the relationship issubstantially one-to-one when the number of ventricular depolarizationsis more than the number of atrial depolarizations but is less than asecond specified threshold depolarization difference value.

In Example 18, the subject matter of one or any combination of Examples11-17 optionally includes calculating a net change over N depolarizationintervals, where N is an integer, and declaring a change in adepolarization interval when the calculated total net interval changeexceeds a specified threshold value.

In Example 19, the detecting an episode of tachyarrhythmia of one or anycombination of Examples 11-18 optionally includes detecting atachyarrhythmia episode when a determined depolarization rate orinterval satisfies a lowest tachyarrhythmia detection threshold rate orinterval.

In Example 20, the subject matter of one or any combination of Examples11-19 optionally includes delaying anti-tachyarrhythmia therapy when A-Adepolarization interval durations and V-V interval durations remainunchanged during the episode.

Additional Notes

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention can be practiced. These embodiments are also referred toherein as “examples.” All publications, patents, and patent documentsreferred to in this document are incorporated by reference herein intheir entirety, as though individually incorporated by reference. In theevent of inconsistent usages between this document and those documentsso incorporated by reference, the usage in the incorporated reference(s)should be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In the appended claims, the terms “including” and“in which” are used as the plain-English equivalents of the respectiveterms “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, or process that includes elements in addition to thoselisted after such a term in a claim are still deemed to fall within thescope of that claim. Moreover, in the following claims, the terms“first,” “second,” and “third,” etc. are used merely as labels, and arenot intended to impose numerical requirements on their objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code can form portions of computerprogram products. Further, the code can be tangibly stored on one ormore volatile or non-volatile computer-readable media during executionor at other times. These computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAM's), read onlymemories (ROM's), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. An apparatus comprising: an implantable cardiac signal sensingcircuit, configured to provide a sensed depolarization signal from aventricle and a sensed depolarization signal from an atrium; and acontroller circuit communicatively coupled to the implantable cardiacsignal sensing circuit, wherein the controller circuit includes: aone-to-one detector circuit configured to: measure cardiacdepolarization intervals of the atrium and the ventricle; and determinewhether a relationship of atrial (A-A) depolarizations to ventricular(V-V) depolarizations is substantially one-to-one; a first countercircuit and a second counter circuit; and a tachyarrhythmiadiscrimination circuit configured to: detect an episode oftachyarrhythmia while the relationship atrial depolarizations toventricular depolarizations is substantially one-to-one; increment thefirst counter when detecting one of a shortening or prolonging of a V-Vinterval that is immediately preceded by the same one of a detectedshortening or prolonging of an A-A interval during the episode;increment the second counter when detecting one of a shortening orprolonging of an A-A interval during the episode that is immediatelypreceded by the same one of a shortening or prolonging of a V-V intervaland an interval from a ventricular depolarization to an atrialdepolarization (V-A) is greater than a specified threshold V-A intervalvalue; classify the episode as VT when the count of the second counterexceeds the count of the first counter by a specified threshold count;and provide the classification of the tachyarrhythmia episode to a useror process.
 2. The apparatus of claim 1, wherein the tachyarrhythmiadiscrimination circuit configured to classify the episode as SVT when acount of the first counter exceeds a count of the second counter by thespecified threshold count.
 3. The apparatus of claim 1, wherein theone-to-one detector circuit is configured to: monitor cardiacdepolarization intervals as they occur in real time; continue themonitoring while the relationship is determined to be substantiallyone-to-one and a difference between the count of the first counter andthe count of the second counter is less than the specified thresholdcount; and wherein the controller circuit is configured to initiatestorage of at least one of an electrogram and a marker when at least oneof the relationship is determined to be different than substantiallyone-to-one or the relationship is determined to be substantiallyone-to-one and the difference between the count of the first counter andthe count of the second counter exceeds the specified threshold count.4. The apparatus of claim 1, wherein the one-to-one detector circuit isconfigured to deem that the relationship of atrial depolarizations toventricular depolarizations is substantially one-to-one when thedifference between a number of atrial depolarizations and a number ofventricular depolarizations during the episode is less than a specifiedthreshold depolarization difference value.
 5. The apparatus of claim 4,wherein the cardiac signal sensing circuit is configured to sense adepolarization during a device-specified refractory period, and whereinthe one-to-one detector circuit is configured to include thedepolarization in the one-to-one determination unless determining thatthe sensed depolarization is a far-field sensed event.
 6. The apparatusof claim 4, wherein the one-to-one detector circuit is configured todeem that the relationship of depolarizations is substantiallyone-to-one during the episode when: the number of atrial depolarizationsis more than a number of detected ventricular depolarizations but isless than first specified threshold depolarization difference value; andthe number of ventricular depolarizations is more than a number ofdetected atrial depolarizations but is less than a second specifiedthreshold depolarization difference value.
 7. The apparatus of claim 1,wherein the one-to-one detector circuit is configured to deem that therelationship of atrial depolarizations to ventricular depolarizations issubstantially one-to-one when the detected ventricular rate differs fromthe detected atrial rate by less than a specified rate difference. 8.The apparatus of claim 1, wherein the tachyarrhythmia discriminationcircuit cancels one-to-one monitoring when detecting a depolarizationrate or depolarization interval that satisfies a ventricularfibrillation (VF) detection rate threshold or VF detection intervalthreshold.
 9. The apparatus of claim 1, wherein the tachyarrhythmiadiscrimination circuit is configured to detect a tachyarrhythmia episodewhen a determined depolarization rate or interval satisfies a lowesttachyarrhythmia detection threshold rate or interval.
 10. The apparatusof claim 1, including a therapy circuit communicatively coupled to thecontroller circuit and configured to provide at least one ofcardioversion shock therapy, defibrillation shock therapy, andanti-tachyarrhythmia pacing (ATP) therapy, and wherein the controllercircuit is configured to delay delivery of anti-tachyarrhythmia therapywhen A-A depolarization interval durations and V-V interval durationsremain unchanged during the episode.
 11. A method comprising: monitoringcardiac depolarization intervals in an atrium and in a ventricle of aheart of a subject using an implantable medical device (IMD); detectingan episode of tachyarrhythmia using the IMD; determining that arelationship of atrial (A-A) depolarizations to ventricular (V-V)depolarizations is substantially one-to-one during the episode;incrementing a first counter when detecting one of a shortening orprolonging of an A-A interval that immediately precedes the same one ofa shortening or prolonging of the V-V interval during the episode;incrementing a second counter when detecting one of a shortening orprolonging of a V-V interval that immediately precedes the same one of ashortening or prolonging of the A-A interval during the episode and aninterval from a ventricular depolarization to an atrial depolarization(V-A) is greater than a specified threshold V-A interval value;classifying the episode as ventricular tachycardia (VT) when the countof the second counter exceeds the count of the first counter by aspecified threshold count; and providing the classification of thetachyarrhythmia episode to a user or process.
 12. The method of claim11, including: classifying the episode as supra-ventricular tachycardia(SVT) when a count of the first counter exceeds a count of the secondcounter by a specified threshold count.
 13. The method of claim 11,including: monitoring cardiac depolarization intervals as they occur inreal time; continuing the monitoring while the relationship isdetermined to be substantially one-to-one and a difference betweencounts of the first counter circuit and the second counter circuit isless than the specified threshold count; and initiating storage of atleast one of an electrogram and a marker when at least one of therelationships is determined to be different than substantiallyone-to-one or the relationship is determined to be substantiallyone-to-one and the difference between the count of the first counter andthe count of the second counter satisfies the specified threshold count.14. The method of claim 11, wherein determining a relationship of atrialdepolarizations to ventricular depolarizations includes deeming that therelationship is substantially one-to-one when the difference between anumber of atrial depolarizations and a number of ventriculardepolarizations during the episode is less than a specified thresholddepolarization difference value.
 15. The method of claim 14, including:sensing a depolarization during a device refractory period; andincluding the depolarization in the one-to-one determination unlessdetermining that the sensed depolarization is a far-field sensed event.16. The method of claim 14, wherein deeming that the relationship issubstantially one-to-one includes: deeming that the relationship issubstantially one-to-one when the number of atrial depolarizations ismore than the number of ventricular depolarizations but is less than afirst specified threshold depolarization difference value; and deemingthat the relationship is substantially one-to-one when the number ofventricular depolarizations is more than the number of atrialdepolarizations but is less than a second specified thresholddepolarization difference value.
 17. The method of claim 11, whereindetermining a relationship of atrial depolarizations to ventriculardepolarizations includes deeming that the relationship is substantiallyone-to-one when the detected ventricular rate differs from the detectedatrial rate by less than a specified rate difference.
 18. The method ofclaim 11, including: calculating a net change over N depolarizationintervals, where N is an integer; and declaring a change in adepolarization interval when the calculated total net interval changeexceeds a specified threshold value.
 19. The method of claim 11, whereindetecting an episode of tachyarrhythmia includes detecting atachyarrhythmia episode when a determined depolarization rate orinterval satisfies a lowest tachyarrhythmia detection threshold rate orinterval.
 20. The method of claim 11, including delayinganti-tachyarrhythmia therapy when A-A depolarization interval durationsand V-V interval durations remain unchanged during the episode.